The present invention relates to control systems which operate with redundant logic channels, and more particularly where these redundant channels are to be physically and electrically independent. Such redundant control systems are employed in nuclear power plants as safety control systems for continued safe operation.
It has been the practice to use photoelectric devices to maintain the physical and electrical insulation between the redundant channels, as is taught by U.S. Pat. No. 3,888,772, owned by the assignee of the present invention. Earlier systems interconnected the separate logic channels with either relays or transformers to provide the isolation.
Electro-optical devices are well known in which a birefringent crystal is modulated by an applied electric field to vary the light transmission characteristic of the crystal. These devices have been used as electrically controlled switches as described in representative U.S. Pat. Nos. 3,069,973; 3,027,806; and 3,531,179.